1. Field of the Invention
The present invention relates to an image recording material which can be used as a planographic printing plate. More particularly, the present invention relates to a negative type image recording material suitably used as a planographic printing plate which is capable of directly producing a printing plate using an infrared laser based on digital signals output from a computer or the like.
2. Description of the Related Art
Conventionally, as systems for producing a form plate directly from digital computer data, there have been proposed (1) a system using an electrophotographic method; (2) a system using a photopolymerizable compound, which polymerizes upon being exposed to a laser which emits blue or green light; (3) a system using a recording material in which a salt is laminated on a photosensitive resin; and (4) a system using a silver salt diffusion transfer method.
However, the system using an electrophotographic method (1) above has complicated image formation processes such as charging, exposure, developing, and the like and therefore the apparatus thereof becomes sophisticated and large. In a system using a photopolymerizable compound (2) above, since a form plate which is highly sensitive to blue or green light is used, it is difficult to handle in an illuminated room. In methods (3) and (4), since a silver salt is used, there are the disadvantages that processes such as developing and the like become complicated and the waste solution naturally contains silver.
In recent years, laser technologies have developed remarkably. In particular, high output and compact solid-state lasers and semiconductor lasers emitting infrared rays of a wavelength of 760 nm to 1,200 nm are readily available. These lasers are very useful as a light source for recording in the direct production of a form plate from digital computer data. However, since most practical useful photosensitive recording materials are sensitive to visible light having a wavelength of 760 nm or less, image recording cannot be carried out with these infrared lasers. Therefore, a material recordable with an infrared laser is desired.
As an example of the image recording materials capable of recording images by the use of an infrared ray laser, a recording material comprising an onium salt, a phenol resin and a spectral sensitizing agent is disclosed in U.S. Pat. No. 4,708,925. However, the image recording material is a positive type recording material utilizing the dissolution prevention effect, generated by the onium salt and the phenol resin, with respect to the developer. On the other hand, examples of negative type image recording materials include a recording material comprising an onium salt, a resol resin, a novolak resin, and an infrared ray absorbing agent disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-20629. According to the image recording material, a positive image is obtained only with laser exposure, but by conducting a heat treatment after the laser exposure, a negative image can be obtained. In general, in order to obtain a negative image, a coated film should not remain on unexposed portions, non-image formation portions, after developing. When the image recording material disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-20629 is heat treated after exposure under mild conditions, positive type characteristics of the recording material become difficult to eliminate and a coated film tends to remain on the unexposed portions. Accordingly, a printing plate utilizing this type of image recording material suffers from the problem of staining at the time of printing. Furthermore, the printing plate using this type of image recording material lacks film strength in the image portion and consequently printing durability at the time of printing is insufficient.